Metallic flat gasket

ABSTRACT

The invention relates to a metallic flat gasket comprising two or more metallic gasket layers ( 2, 3, 3′, 3 ″), of which a shortened gasket layer ( 2 ) has a smaller surface area than the at least one other gasket layer. At least one through-opening ( 4 ) extending through the gasket layers is surrounded by a self-contained bead ( 5 ) which is introduced into one of the relatively extensive gasket layers ( 3 ), the shortened gasket layer ( 2 ) leaving free an outer edge region ( 6 ), which does not comprise the bead ( 5 ), of the relatively extensive gasket layer. At least one structuring ( 7 ) is present in one of the gasket layers, in a region of the gasket in which the shortened gasket layer ( 2 ) is present or directly laterally adjoining this region adjacent to the position of the bead ( 5 ), said structuring protruding beyond at least one surface of the gasket layer and consisting of a large number of alternating elevations ( 31 ) and depressions ( 32 ) which are introduced into the gasket layer, the structuring ( 7 ) being present at least in certain portions in the circumferential direction around the through-opening ( 4 ).

The invention relates to a metallic flat gasket comprising at least twogasket layers through which at least one through-opening extends. Of thegasket layers, one is shortened compared to the others and has a smallersurface area. A bead, which surrounds the through-opening in aself-contained manner, is provided in a relatively extensive gasketlayer. The shortened gasket layer is not present in an outer edgeregion, radially externally adjoining the bead, of the relativelyextensive gasket layer. Metallic flat gaskets of this type are used forexample as a gasket in the region of internal combustion engines and theexhaust tract thereof, in particular as exhaust gas manifold gaskets oras cylinder head gaskets.

In order to allow the bead reliably to seal the through-opening, it isgenerally necessary for the bead to be loaded uniformly and withsufficiently high compression. This applies in particular to the sealingof combustion chamber openings in cylinder head gaskets and in this caseespecially to cylinder head gaskets used in engines with open-deckdesigns. There have been proposed, to increase the compression in theregion of the bead, cylinder head gaskets in which an additional layershaped in a spectacle-like manner is present around the combustionchamber opening. This additional layer is often referred to as the“shim”. A shim of this type is a layer which is shortened relative tothe remaining gasket layers and, viewed from the combustion chamberopenings, often reaches only just beyond the edge of the feet of theouter bead and may reach the water jacket. Usually it is a planar layerwhich serves exclusively to increase the material thickness in theregion of the combustion chamber beads. The aim of the shim is thereforea material thickening in the contact region of the beads, whichthickening places the beads in a main loading connection and increasesthe compression in the region of the beads. Examples of cylinder headgaskets comprising a shim are described for example in EP 1065417 A2.

In recent times use has increasingly been made of engines in which—inorder to save weight—the motor block is made of light metals or metalalloys such as aluminum or aluminum/magnesium. In addition the motorblock has been reduced in a skeleton-like manner to the supportingparts, whereas the openings—for example the cooling water openings inthe open-deck engines—are very large. This design leads to an increasein temperature and reduced rigidity of the upper side of the motor blockand requires cylinder head gaskets which, even at a relatively lowscrewing force, reliably seal the gap between the motor block andcylinder head. Critical in the case of conventional cylinder headgaskets comprising a shim is in this regard, in particular, the factthat in the event of local weak points in the motor block andinsufficient component rigidity, improvement with regard to the sealinggap movements and the distribution of compression is then hardlypossible. If the compression is set too high, there is the risk that thebeads will be subjected to excessive compression, lose their elasticityat high temperature and excessive compression and therefore no longerproduce an adequate seal.

There was therefore a need for a metallic flat gasket, in particular acylinder head gasket, of the type described at the outset that leads toreliable sealing even under the disadvantageous conditions of hightemperature and low rigidity of an opposing surface to be sealed. Theobject of the invention is accordingly to devise a metallic flat gasketof this type.

This object is achieved by the metallic flat gasket according to claim1. Preferred embodiments of the flat gasket are described in thesub-claims.

The metallic flat gasket according to the invention has at least twometallic gasket layers. One of the gasket layers is a shortened gasketlayer having a smaller surface area than the at least one other gasketlayer. At least one through-opening, which is surrounded by aself-contained bead which is provided in one of the relatively extensivegasket layers, extends through the gasket layers. The shortened gasketlayer is not present in an outer edge region, which does not comprisethis bead, of the relatively extensive gasket layer. In one of thegasket layers, in a region of the gasket in which the shortened gasketlayer is present or directly laterally adjoining this region adjacent tothe position of the bead and protruding in the direction thereof, atleast one structuring is formed into the gasket layer. This structuringconsists of a large number of alternating elevations and depressions. Inthis case, in a first embodiment, the structuring is present only incertain portions in the circumferential direction around thethrough-opening. In the region of the structuring the overall height ofthe layer, including the height introduced by the structuring, isgreater than the overall height of the layers in the adjacent region inwhich the shortened gasket layer is present. The shortened layer can inthis case project into the structured region, although this is notnecessary.

In a second embodiment the height or width of the structuring changes inthe circumferential direction around the through-opening, thus formingat this location regions in which, as a result of the correspondinglytall structuring, the overall height of the layer is greater than theoverall height of the layers in the adjacent region in which theshortened gasket layer is present.

In a modification of these two embodiments it is possible for thestructuring to be introduced in the shortened layer, in such a way thatin the cross section thereof a structured higher region, an unstructuredlow region and a structured higher region succeed one another.

The structuring of the gasket layer produces locally in a portion aroundthe through-opening a region in which the material thickness is greaterthan it would be without the structuring. This region is expedientlyarranged in such a way that it is located at the location where, in theopposing surface to be sealed (i.e. for example the motor block orcylinder head surface) a site of reduced component rigidity is located.Similarly in a structuring, the height of which changes over thecircumference thereof, the greater height will be used in the regions ofreduced component rigidity. The material thickening produced by thestructuring ensures that sufficient compression can be achieved in thiscritical region.

Critical regions of reduced component rigidity are located, in the caseof engines, for example in the region between adjacent cylinder bores orelse in the region of undercuts in the cylinder head. Accordingly, thestructuring according to the invention is preferably arranged in theseregions. The critical regions can however also be all remaining regionsaround a through-opening in a gasket in which (for example owing to thelow material thickness, defects in manufacture (for example surfaceirregularities) or for other reasons) reduced component rigidities orlocal structural weak points of the component are to be expected in theadjacent opposing surface to be sealed.

The structuring can be present either between the bead andthrough-opening or on the side of the bead that is remote from thethrough-opening or else on both sides of the bead. In a preferredembodiment the longitudinal extent of the structuring reaches only incertain portions around the through-opening, but does not surround saidthrough-opening entirely, but is instead limited to the particularlycritical regions such as, for example, a web region between adjacentthrough-openings. The structuring—in general simply for reasons ofspace—is generally smaller in its width extent than in its longitudinalextent. Preferably, it is configured in a strip-like manner and inparticular in the form of an annular segment. In the latter case thestructuring expediently follows the course of the through-opening or thebead surrounding said through-opening.

In a preferred variation of the invention the structuring is configuredin such a way that its alternating elevations and depressions extendlinearly. An undulatory structuring of the corresponding region of thegasket layer is formed in this way. Particularly preferably, theelevations and depressions are in this case configured in the form ofconcentric ring segments. The cross section of the wave crests and wavetroughs of the undulatory profiling in a section in the radial directioncan in principle also be configured in any desired manner. Preferredshapes have a sinusoidal, trapezoidal or zigzag-shaped cross-sectionalprofile. Modifications of these shapes, for example with flanks risingat differing degrees of steepness, flattened peaks, etc. are howeveralso conceivable. The cross-sectional shape can be the same for all wavecrests and wave troughs or differ for individual wave crests and/or wavetroughs. It is also possible to vary the cross-sectional shape in thecourse of a single wave crest or wave trough. Such structurings withannularly closed elevations and depressions are already known asstoppers for beads which seal an opening in a cylinder head gasket, andare conventionally referred to as wave stoppers. Wave stoppers of thistype have previously been described in WO 01/96768 A1 and DE102004011721 A1 in the name of the applicant. This type of structuringand also the type of manufacture can be used in the described manner forthe structuring of the present invention. Reference may therefore bemade to the content of the aforementioned documents.

In an alternative embodiment the elevations and depressions of thestructuring are arranged on at least one set of virtual straight linesextending substantially parallel over the total extent of thestructuring. Preferably, the elevations and depressions alternate inthis case transversely to the direction of extension of the lines. Astructuring of this type is likewise in principle already known formetallic flat gaskets and has likewise been described by the applicantof the present invention, namely in European patent application07008321.7, whose priority is claimed in this respect. The elevationsand depressions are preferably trapezoidal, triangular, rounded orrectangular in cross section.

The set of straight lines extending substantially parallel are virtuallines. Although these lines continue over the entire surface area of thestructuring, elevations or depressions do not necessarily also have tobe present at each point of these lines. For example, the virtual linescan intersect the region of an opening or a sealing element in which noelevations and depressions are present. In such a case elevation(s)and/or depression(s) extend on a virtual straight line up to the openingor the sealing element, where they are broken off and then continueagain on the opposing side on the same straight line. The term “a set ofstraight lines extending substantially parallel” refers, in the case ofa substantially parallel course of the lines, to a departure fromparallelism of at most 5° and in particular at most 2°.

The elevations and depressions in the compensating region of the flatgasket according to the invention are produced preferably by embossing.If use is in this case made of two complementary embossment forms, theelevations of which are in each case laterally offset relative to theelevations of the other embossment form and engage with the depressionsin the opposing form, there results a structured region, the elevationsof which protrude beyond both surfaces of the gasket layer. The materialthickening produced by the structuring therefore affects both surfacesof the gasket layer. In order to make the material thickening in thestructured region effective fully for the neighboring gasket layer, thestructured region of the structured gasket layer can be for examplecranked in the direction of the neighboring gasket layer. Likewise,asymmetrical tool configuration allows the elevations of the structuredregion to protrude only beyond one surface of the structured gasketlayer.

As a whole, the embossed region has in its cross section elevations,depressions and a respective region of transition, also referred to asthe flank, between adjacent elevations and depressions. The structuresare generated preferably by means of compression. In this case thematerial in the region of the flank is reduced relative to the materialthickness in the region of the elevations and depressions, thusrigidifying the compensating region. The material tapering in the flankregion is in this case at least 8%, preferably at least 10%,particularly preferably at least 13% and in particular at least 15%relative to the material thickness in the region of the adjacentelevation or depression.

Although at first sight, the elements of the structure may resemble abead, they have less resiliency than the latter, which is also due tothe tapering. Moreover, their width is smaller than the one of a bead.This can for instance be shown with respect to the thickness of thegasket layer. The ratio between the width of a bead (starting from thepoint where it raises out of the plane) and the thickness of theunstructured gasket layer is at least 6, preferably at least 7. Incontrast, the ratio between a period of the structure is at the most 4,preferably between 2.5 and 3.5.

The structured region can, in addition to the above-mentioned elevationsand depressions alternating transversely to the direction of extensionof the virtual straight lines, also be configured in such a way thatelevations and depressions on mutually adjacent lines are in each casearranged offset relative to one another. Such cases give rise to achessboard-like structure of elevations and depressions. Preferably, thedepressions extend along at least two intersecting sets of virtualstraight lines. Particularly preferred is an arrangement on virtualstraight lines which intersect at right angles.

In principle, it is also possible for the virtual straight lines tointersect not in the structured region, but rather outside; thisproduces regions having a differing structuring orientation. Alsopossible are transitions in which a region in which exclusively thefirst set of virtual straight lines forms elevations and depressions isfollowed by a region in which a first and a second set of virtualstraight lines can be seen as elevations and depressions and which isadjoined by a region in which only the second set of virtual straightlines is embodied in elevations and depressions.

On the whole, it should be noted that the region of the structuring is aregion of increased plastic deformation of the gasket layer that has noor only very little elasticity. Accordingly, the structures of thestructuring are much smaller (for example compared to conventionalelastically deformable beads). Preferably, the height of the structuringis set in such a way that the elevations protrude by from 0.01 to 0.4 mmbeyond the gasket layer into which they are introduced. The heightdepends in this case primarily on whether or not the structuringoverlaps the shortened layer. In the former case (overlap) the height ispreferably between 0.01 and 0.05 mm, in the latter case between 0.09 and0.40 mm. The height can be set during the elaboration of the elevationsfrom the gasket layer or as a result of the fact that the elevationswhich are generated are planished, after production thereof, in certainportions or over the entire structured region. The distance betweenadjacent parallel elevations is expediently in a range of up to 2.0 mm,preferably up to 1.6 and particularly preferably up to 1.3 mm, inparticular up to 0.7 mm. If the elevations do not have any peak point,but rather a flattened peak region, the distance between the centerpoints of these peak regions is measured, in all cases in a plane whichis parallel to the plane of the gasket layer.

The structuring in the structured region imparts to the structured layerat this location a greater thickness than the thickness of the originalgasket layer, i.e. of the planar gasket layer prior to the introductionof the structuring. The height of the structuring is in this casemeasured as the distance between two tangential planes each extendingparallel to the plane of the non-deformed gasket layer. The distance istherefore measured between the plane of the untreated gasket layer and aplane resting on the elevations protruding beyond this surface of thegasket layer. In this case the height of the elevations does not have tobe uniformly high over the entire structured region. Depressions areregions which are lower than the elevations, i.e. not necessarilyregions which are sunk into the plane of the undeformed gasket layer.

The embossing of the structured region allows the structuring to be setvariably in a very broad range without the need for additional material.The structuring does not—as stated hereinbefore—have to be configureduniformly over the entire structured region, but can rather vary overthe surface area of the structured region. A topography can therefore begenerated in the structured region which facilitates purposefulinfluencing of the compression of the bead layer and allows adaptationto the opposing surfaces to be sealed and the component rigiditiesthereof. Expediently, the topography in the structured region is in thiscase selected in such a way that the sealing gap movement is as uniformas possible.

The structuring can in principle be configured in any desired one of thegasket layers. One possibility is to configure the structuring in theshortened gasket layer. As the shortened gasket layer has only acomparatively short spatial extent, the structuring will generallyextend along one or both of the outer edges thereof, whereas theinterior is planar in its configuration and serves as a contact regionfor the bead. Another possibility is for the structuring to beconfigured in at least one of the relatively extensive gasket layers. Itis then located either in a region in which the shortened gasket layeris present or directly laterally adjoining an outer edge of theshortened gasket layer. The term “directly adjoining” means in this casethat the distance between the edge of the structuring and the outer edgeof the shortened gasket layer is no more than 3 mm, preferably no morethan 2 mm. As mentioned hereinbefore, the structuring can also bepresent on both sides of the bead.

If the structuring configured in a relatively extensive gasket layeroverlaps the shortened gasket layer, there is produced in the region ofthe structuring a local thickening, in the region of which the sums ofthe thicknesses of all gasket layers present therein is greater than thesum of the thicknesses of all gasket layers in a region adjoining thestructuring. A thickened region, which can accommodate increasedcompression and reduce the compression acting on the bead, is in thisway formed laterally adjacent to the bead. Purposeful selection of theheight of the structuring allows the sealing gap movement to be limitedin this case. It is also possible to configure structurings in both theshortened and a relatively extensive gasket layer. The structurings arethen preferably arranged in regions which are laterally offset relativeto one another.

If, on the other hand, the structuring does not overlap the shortenedgasket layer, the structuring must be configured in such a way that theoverall thickness in the region of the structuring is greater than inthe adjacent region comprising the shortened layer.

In the simplest embodiment the metallic flat gasket according to theinvention has in the shortened gasket layer just a singlethrough-opening which is enclosed by a bead. The shortened gasket layeris then predominantly annular and in particular circular. In most casesthe metallic flat gasket will however have a plurality ofthrough-openings which are each surrounded by a bead which is providedin the relatively extensive gasket layer. In the case of a plurality ofthrough-openings, the shortened gasket layer is preferably configured ina spectacle-like manner, such as is in principle already known in theart for shims (cf. EP 1065417 A2).

If the metallic flat gasket according to the invention has a pluralityof through-openings, each surrounded by a bead, and if the region of thelowest force introduction is at the same time located in the regionbetween the through-openings, the structuring will preferably be presentin this region of reduced force introduction, i.e. between adjacentthrough-openings and in particular only at this location. In anarrangement of this type, allowance can be made for the reducedcomponent rigidity in the narrow web region between adjacentthrough-openings (for example the cylinder bores in a motor block) and asuitable setting of the compression acting on the bead can be ensured atthis location. If there is only a very short distance between adjacentthrough-openings, it is also possible for the beads to merge in the webregion between the through-openings to form a single bead portion. Insuch cases there is no longer any space for a structuring arrangedbetween the feet of the beads which are remote from thethrough-openings, at least in the central region where the width of theweb is most narrow. However, structurings can be arranged in one or bothweb edge regions which are adjacent to the central region, as here theedges of the through-openings and the beads depart from one anotheragain.

In addition or as an alternative to the arrangement of the structuringin the web region between adjacent through-openings, the arrangement canin principle be present in the regions in which reduced effective forceintroduction results from the interplay of the screwing force introducedand the local rigidity of the components to be sealed. More than onesurface-structured region can also be present around a through-opening.

In a simple configuration the metallic flat gasket according to theinvention has, in addition to the shortened gasket layer, just onefurther relatively extensive gasket layer into which the at least onebead is then introduced. The structuring can be located in either theshortened and/or the relatively extensive gasket layer.

If the metallic flat gasket has, in addition to the shortened gasketlayer, more than one relatively extensive gasket layer, the relativelyextensive gasket layers can be the same or different in theirconfiguration. For example the bead can be introduced into one, whereasthe other has the structuring and if appropriate also a bead for sealingthe through-opening. If it has no bead, the layer is for example a layerwhich is planar apart from the structuring, which is usually referred toas a spacer layer and contains no beads, folds or the like over itsentire extent and serves predominantly to set the overall thickness ofthe composite structure consisting of a plurality of gasket layers.Alternatively, the structuring and bead are located in the samerelatively extensive gasket layer.

Preferred is a variation of the flat gasket according to the inventioncomprising at least three gasket layers in which at least two relativelyextensive gasket layers have mutually complementary beads and inparticular beads which are arranged in a mirror-inverted manner withrespect to one another. In this case the beads can be arranged withtheir bead apices pointing toward one another or else pointing away fromone another. If respective beads for sealing the through-opening arepresent in a plurality of relatively extensive gasket layers, thesegasket layers are preferably made of the same material in order toobtain the same spring constant for the beads in the gasket layers. Theuse of the same materials for the gasket layers also facilitatesmanufacture and reduces costs. It is however also possible to usediffering materials for both gasket layers and—if the same springconstant is desired for the beads surrounding the through-opening—to setthis spring constant by shaping the beads or in another manner known perse.

Irrespective of this, it is in principle possible to vary the shape ofthe bead in order to change its properties in the circumferentialdirection and optimally to adapt them to the predetermined conditions.In a manner known per se, preferably at least one of the followingproperties is in this case changed in the circumferential direction: thecross-sectional shape of the bead, its height and its width. Inprinciple, it is also possible to adapt the bead properties by means ofchemical treatment, laser irradiation or heat treatment. In regions ofreduced force introduction, the rigidity of the bead can in this case bepurposefully increased.

Furthermore it is possible—especially if the structuring is provided inthe shortened layer and if, in the case of a gasket comprising at leasttwo relatively extensive layers with full beads, the bead apices thereofpoint toward one another—to provide a cranking in at least one of thebeaded layers between the full bead and the combustion chamber, theheight of the cranking being much less—for example ⅓ the height—than theheight of the bead or to incline this portion out of the plane in such away that it points in the direction of the other extended layer. Thesemeasures can bring about an additional preseal with respect tocombustion gases.

In the so-called “hinterland” of the flat gasket according to theinvention—i.e., in the outer edge region where the shortened gasketlayer and the structuring are not present—the flat gasket can inprinciple be configured as is known in the art. In principle, theshortened gasket layer is configured to be only as large as is necessaryfor the function of the gasket. Its extent is determined mainly by thedimensions of the beads which are present in the same region as theshortened gasket layer or by the dimensions of the water jacket.Generally the shortened gasket layer has a width (e.g. from thecombustion chamber) which is not greater than seven times the distancebetween the feet of the bead in its region. As mentioned hereinbefore,further openings can be present in the “hinterland” of the gasket. Inthe case of cylinder head gaskets, these are openings for fasteningmeans, oil and cooling liquid. These openings can in each case besealed, as is conventional in the prior art, using sealing elements. Usemay in this case in principle be made of the sealing elements which areconventional in the prior art, i.e. for example elastomer sealingelements and/or beads which are introduced into the at least onerelatively extensive gasket layer. The elastomer can be applied to thegasket layer on one or both sides or sprayed onto the opening edge. Thesealing elements of the “hinterland” can also be configured in a mannerknown per se as separate regions (what are known as inserts) which areinserted into the gasket layer.

The metallic flat gasket according to the invention can be made of thematerials previously conventional for metallic flat gaskets and usingthe standard production tools. Spring steel is expediently used as thematerial of those gasket layers into which beads are introduced assealing elements for through-openings. For the other gasket layers,which have no beads, softer steel, for example construction steel, canbe used. High-grade steels or carbon steels can be used in this case. Inaddition, individual gasket layers or all of the gasket layers of theflat gasket according to the invention can be coated wholly or partly,on one side or on both sides. In this case the coatings known per se canbe used to improve the microsealing, the sliding friction properties,etc. The coating can be applied after the embossment or precoated, evencoil-coated material can be embossed.

The individual gasket layers of the flat gasket according to theinvention can be joined together in a manner conventional in the priorart, for example by riveting, welding (spot-welding, laser-welding,etc.), by clinching, soldering, bonding, clipping-on, etc.

The metallic flat gasket according to the invention is suitable for alarge number of applications, for example as a flange gasket, exhaustgas manifold gasket or the like. The term “flat gasket” expresslyincludes three-dimensionally deformed gaskets of the type deformed froma two-dimensional body, i.e. for example conical gaskets. The flatgasket according to the invention is particularly suitable as a cylinderhead gasket, the through-openings corresponding to the combustionchamber openings. A cylinder head gasket of this type is particularlysuitable for open-deck engines in which the water openings are opentoward the upper side of the motor block. The shortened gasket layerperforms the function of a conventional shim. In contrast to the priorart, a gasket according to the invention adapts, on account of thepurposeful arrangement of the structuring in regions in which structuralweak points or a reduced rigidity of the components to be sealed arepresent, more effectively to the opposing surfaces to be sealed andensures more permanent tightness.

The invention will be described hereinafter in greater detail withreference to the drawings. The figures are intended exclusively toillustrate preferred exemplary embodiments, without the invention beingrestricted thereto. In the figures like reference numerals denote likeparts. In the figures:

FIG. 1 shows in partial figures a-f schematic plan views onto examplesof a metallic flat gasket based in each case on the example of acylinder head gasket;

FIGS. 2 to 18 are schematic partial cross sections of various exemplaryembodiments of cylinder head gaskets according to the invention in aregion around a combustion chamber opening in the gasket according toFIG. 1, and

FIG. 19 is a schematic partial cross section through a structuring,which is provided with elevations and depressions, of a metallic flatgasket according to the invention.

FIG. 1-a shows a metallic cylinder head gasket 1 in a plan view onto arelatively extensive gasket layer 3 extending substantially over theentire surface of the opposing surfaces to be sealed (i.e. of a motorblock and a cylinder head). The relatively extensive gasket layer 3 isfor example made of spring steel. Formed therein are variousthrough-openings, namely inside the gasket layer three through-openings4 which are arranged next to one another and correspond to thecombustion chamber openings. Around the combustion chamber openings 4,various further openings 8 are present in the second gasket layer 3toward the edge 9 of the gasket 1. These correspond to screw openings,whereas oil openings and openings for cooling liquid are not shown inthe present figure for the sake of clarity. Such openings can however beconfigured in accordance with the prior art.

The through-openings 4 are each surrounded by a bead 5 enclosing saidthrough-openings. The course of the beads 5 is in this case specified bytwo lines which illustrate the position of the bead legs. Thecross-sectional shape of the beads 5 may in principle be of any desiredshape. In FIGS. 2 to 18 the beads 5 have a trapezoidal cross section.Beads having a rounded cross section can however also be used.

On the side of the bead 5 that faces the combustion chamber 4, astructuring 7 extends at a distance from the bead but reaching up to theedge 40 of the combustion chamber. Whereas the beads, also for reasonsof space, are guided through the web region 30 in such a way that ineach case only the leg facing the edge 40 of the combustion chamber iscontinued, whereas the other leg is extended to the corresponding beadleg of the bead of the adjacent combustion chamber, the remaining spaceis sufficient to guide the structuring 7 with unreduced width throughthe web region 30, so any structuring 7 annularly encloses a combustionchamber 4.

Details A and B illustrate the course of the structuring 7 in apreferred embodiment along the edge 40 of the combustion chamber opening4. The partial images show also the structure of the beads 5 comprisingtwo respective bead legs 50, 51 and a bead apex 52 located therebetween(two of the four lines coincide in the overviews). The structuring 7 isconfigured over its entire course in the form of alternating elevations31 and depressions 32 extending on virtual lines which are parallel toone another. In the exemplary embodiment shown, these structures 7 takeup an approximately circular region extending concentrically with acombustion chamber opening 4. As a result, the direction of extension ofthe elevations 31 and depressions 32 extends approximately parallel inportions (in proximity to detail A) and in other portions transversely(see detail B) to the edge 40 of the combustion chamber opening 4 or tothe bead 5. A large region of transition extends in each case betweenthese aforementioned portions. In the case of an identicalcross-sectional configuration, the structuring causes transversely tothe bead greater rigidification of the structured regions than thestructuring parallel to the bead. The compensation for the differingcomponent rigidities may thus in some cases be achieved without furthermeasures. Furthermore purposeful configuration of the density of theelevations and depressions or other parameters of their cross-sectionalstructure allows purposeful compensation for the component rigidities tobe achieved.

Unlike in FIG. 1-a, in the following exemplary embodiments 1-b to 1-ethe bulk of the structuring extends on the side of the bead 5 that isremote from the combustion chamber 4. In the example of FIG. 1-b astructuring 7 has in this case been dispensed with in the web region 30.The structuring 7 has however been widened in entrance regions 34 to theweb regions 30.

In comparison to the exemplary embodiment of FIG. 1-b, in that of FIG.1-c parts of the web region 30—in addition to the enlarged entranceregion 34—are also structured. The structuring is in this case locatedbetween the continuous bead legs. The narrowest region of the web doesnot however have a structuring owing to lack of space.

In the exemplary embodiment according to FIG. 1-d as well, the course ofthe structuring according to FIG. 1-b is supplemented with a structuring7 in the web region 30. In this case, however, the structuring extendson the side of the embodied bead that faces the combustion chambers andruns through all of the web region.

Furthermore FIG. 1-e demonstrates that it is not necessary in everyapplication for the structuring 7 to enclose the combustion chambers 4annularly or in a spectacle-like manner. In this case the entranceregions 34 to the web regions 30 do not have a structuring either.Furthermore the detailed views of FIG. 1-e show that the two sets, whichare present in the example, of virtual straight lines, which arearranged substantially orthogonally with respect to one another, canintersect in the regions in which both sets actually form elevations anddepressions, as is shown by way of example in region A in detailed viewF. Detailed view E shows on the contrary a region of transition inwhich, starting from a structuring which maps only the parallel linesextending from the bottom left to the top right in elevations anddepressions (region C), a turning, similar to a miter, of the elevationsand depressions which are actually present takes place, so theelevations and depressions extend continuously on the second set ofparallel lines from bottom right to top left (region B). The regions oftransition as shown in detailed views E and F are in this casepreferably located in the region which is remote from the fasteningmeans openings.

Finally FIG. 1-f shows that there are also applications in which thestructuring is restricted to highly limited regions, for example to theactual web region. A peripheral structuring has been dispensed with inthis case owing to the conditions in the respective engine. Similarly inthe example of FIG. 1-e it would be possible, if the engine conditionscalled for this, to dispense with the structuring 7 in the region 39between the broken lines 38 drawn by way of example, if compensation forlow component rigidities is necessary only in the region 37 of thelongitudinal rims.

The examples of FIGS. 1-a to 1-f, for reasons of clarity, show thestructuring in each case in the top gasket layer. As will bedemonstrated hereinafter, the structuring can however also be located ina lower gasket layer—which cannot be seen in the plan views according toFIGS. 1-a to 1-f.

As may be seen in the cross sections of FIGS. 2 to 17, all of thegaskets disclosed therein each have two further gasket layers. Thegasket layers cannot be seen in the plan view of FIGS. 1-a to 1-e, asthey are arranged below the gasket layer 3. The gasket layer 2 arrangedimmediately below the gasket layer 3 is a shortened gasket layer whichis much shorter than the relatively extensive gasket layer 3. Theshortened gasket layer 2 is configured in a spectacle-like manner andextends exclusively in the immediate vicinity around thethrough-openings 4. Its width is in this case up to seven times the sizeof the distance between the feet 50 and 51 of the bead 5.

The shortened gasket layer corresponds to a shim and fully exposes theedge region 6 of the second gasket layer 3. Accordingly, the gasketlayer 2 also contains exclusively through-openings 4, but otherwise nofurther through-openings. In the edge region 6, the flat gasket 1according to the invention consists exclusively of the second gasketlayer 3 and a further relatively extensive gasket layer 3′ arrangedbelow the gasket layer 2. On account of this design, a greater materialthickness is achieved in the region around the through-openings 4 thanin the edge region 6, where the shortened gasket layer 2 is not present.As a result, the compression in the region around the through-openings 4increases, thus allowing improved sealing of the combustion chamberopenings to be achieved at this location by means of the beads 5.

The further gasket layer 3′ likewise has a surface area correspondingsubstantially to the extent of the opposing surfaces to be sealed. It isfor example oriented in the direction toward the motor block. The gasketlayer 3′ also has beads 5′ which each surround one of the combustionchamber openings 4. The shape and course of the beads 5′ correspondfully to those of the beads 5 of the gasket layer 3. The beads 5 and 5′are therefore configured mirror-symmetrically with respect to oneanother and rest against one another, with the exception of the examplefrom FIG. 17, with their bead apices. The material of which the gasketlayer 3′ is made also corresponds to that of the second gasket layer 3.As a result, the beads 5 and 5′ have the same spring characteristic.

As is indicated by the broken lines in FIG. 2, the gaskets according tothe invention can also contain more than three gasket layers. In theexample shown two additional cover layers 3″ and 3′″ are present, ofwhich the former corresponds to the gasket layer 3′ and the latter tothe gasket layer 3. The beads 5″ and 5′″ again extend in amirror-inverted manner with regard to the beads 5 and 5′, respectively,of the respectively adjacent gasket layer. In the example of FIG. 18 thegasket contains a smooth sheet metal layer 100 containing neither thestructuring nor beads. A layer of this type is often configured so as tobe thicker than the remaining layers and can serve to adapt the overallheight of the gasket to the sealing gap to be sealed.

The exemplary embodiments shown in FIGS. 2 to 17 differ from one anotherin terms of the arrangement of the structuring 7. In all cases, however,the structuring 7 serves locally to adapt the gasket to regions of theopposing surfaces that are particularly critical for sealing and, in theexamples shown, specifically to the surface of the motor block or thecylinder head. The structuring 7 is in each case arranged in such a waythat it allows a local increase in compression in the critical region,compared to a situation in which the structuring is not present. Thisincrease in compression is achieved as a result of the fact that, in thecorresponding gasket layer, elevations 31 and depressions 32 areprovided, based on which the thickness of the gasket layer in thestructured region increases relative to the original thickness of thegasket layer (i.e. the thickness prior to structuring). Depending on theembodiment, the surface elevation protrudes beyond just one surface orbeyond both surfaces of the gasket layer.

In the variations shown in FIGS. 2 to 5 and also in FIG. 17, thestructuring is in each case configured in the shortened gasket layer 2and protrudes beyond both surfaces thereof. FIGS. 2 and 3 show thearrangement in a region between the bead 5 and combustion chamberopening 4, FIGS. 4 and 17 show the arrangement on the side of the bead 5that is remote from the combustion chamber opening 4, and FIG. 5 showsthe arrangement on both sides of the bead 5. The structuring 7 islocated in the edge regions of the gasket layer 2. The central region isplanar so as to supply a flat contact region for the beads 5, 5′.

In the gaskets according to FIGS. 6 to 16 the structuring 7 is presentin the relatively extensive gasket layer 3, in FIGS. 9 and 13 to 16 itis additionally present in the further gasket layer 3′. The structuring7 is in each case configured in a strip-like manner and follows in itscourse the course of the adjacent bead. In the gaskets according toFIGS. 6, 8 and 9 the structuring is located between the bead 5 andcombustion chamber opening 4, in FIGS. 7, 10 and 16 on the side of thebead that is remote from the combustion chamber opening 4, and in FIGS.11 to 15 on both sides of the bead 5. Whereas in FIGS. 11 and 12 thetwo-sided structure is introduced in the same gasket layer (3), in FIGS.13 and 14 it is present on each side on another gasket layer (3 and 3′).In FIG. 15 finally both layers (3 and 3′) have structurings 7 on bothsides.

In the examples of FIGS. 6, 7, 11 and 14, as on the side remote from thecombustion chamber in FIG. 13, the structuring 7 is arranged laterallyof the shortened gasket layer 2. There is therefore no overlap betweenthe gasket layer 2, which is completely planar in all of the examples ofFIGS. 6 to 12, and the structuring 7 in the compressed state either. Theheight which is additionally introduced by the structuring 7 into thestructured region is in this case greater throughout than the thicknessof the shortened gasket layer 2. This ensures that the gasket in allcases has its greatest thickness in the structured region. The heightwhich is introduced relative to the region of the beads 5 and 5′therefore corresponds to the height introduced by the structuring intothe structured region less the thickness of the shortened gasket layer2. It is thus possible purposefully to introduce only small cambers bymeans of the structuring. The structuring therefore brings the beadlocally into a secondary loading connection, whereas in the remainingregions it is in a main loading connection.

In FIGS. 8 to 10, 12, 14 to 18, and also in FIG. 13 on the side facingthe combustion chamber, the shortened gasket layer 2 has a larger extentthan in the figures described hereinbefore, so the structuring 7 andshortened gasket layer 2 overlap. The structuring is less deep than inthe previously disclosed examples. The thickness additionally introducedby the structuring 7 in this case is less than the thickness of theshortened gasket layer 2.

If the structuring is provided in the shortened gasket layer 2, thislayer will usually be structured only to such an extent that itsthickness, including the structuring, is less than twice the initialthickness of the metal sheet. This is clear from the examples of FIGS. 2to 5.

In the illustrated examples the structuring 7 consists of elevations 31and depressions 32 which are each arranged in alternation on straightlines. The straight lines are virtual lines extending in parallelarrangement over the entire structured region. These virtual linesintersect in this case also the through-openings 4 and the beads 5surrounding said through-openings. The elevations and depressions are inthis case however present only in the hatched regions. In the preferredembodiment shown in details A and B from FIG. 1-a all elevations arearranged on adjacent parallel lines. It is however also possible toarrange the elevations and depressions on mutually adjacent parallellines so as to be in each case offset, so the elevations and depressionsalternate also in a direction perpendicular to the parallel lines.Overall, this gives rise to a chessboard-like arrangement of theelevations and depressions in the structured region 7.

The height by which the elevations protrude beyond the surface of thegasket layer in the direction of the adjacent bead can be set so as tocorrespond to the desired compression. In this case it is in principlepossible to vary the height of the elevations in the structured region.In this way allowance can be made for the rigidities of the componentsand the compression around the through-openings 4 can be made uniform.Obviously, it is likewise possible, should this be desirable, to set anon-uniform distribution of compression in the region around athrough-opening 4 or from one through-opening to another through-opening4.

As mentioned hereinbefore, the elevations 31 and depressions 32 of thestructuring 7 are produced preferably by embossing. The embossing stepis carried out preferably using an embossing tool having twocomplementary embossment forms. These embossment forms expediently eachhave embossed projections which engage with corresponding depressions inthe complementary embossment form. Elevations and depressions of oneembossment form are therefore arranged offset relative to the elevationsand depressions of the complementary embossment form. If the elevationsand depressions of the complementary embossment forms are each ofsimilar configuration, this tool constellation results in a particulardistribution of material thickness in the region of the machined gasketlayer that is structured with the embossment form. This will beillustrated schematically with reference to FIG. 19.

FIG. 19 shows a detail from a region of a gasket layer, in which astructuring 7 is present. Elevations 31 and depressions 32 are embossedinto this region. The elevations 31 protrude by a height H beyond thesurface of the gasket layer 3. As a result of the embossing, thethickness of the gasket layer 3 in the region of the flanks 36 has beenreduced relative to the thickness of the elevations 31 or depressions32. The thickness D₃₆ in the flank region is therefore less than thethickness D₃₁ of the gasket layer 3 in the region of the elevations ordepressions. This reshaping of the material and reduction of thematerial thickness lead to an increase in the rigidity of the structuredregion. For demonstration purpose, the extent of the flank tapering isexaggerated in FIG. 19. It is frequently between 10 and 25%, inparticular between 13 and 19%. FIG. 19 also indicates that a period ofthe structuring, P, is usually about 2.5 to 3.5 times larger than theoriginal thickness of the gasket layer, H. The ratio P/H in general doesnot exceed 4.

1-24. (canceled)
 25. A metallic flat gasket comprising two or moremetallic gasket layers, of which a shortened gasket layer has a smallersurface area than the at least one other gasket layer, and comprising atleast one through-opening which extends through the gasket layers and issurrounded by a self-contained bead which is provided in one of therelatively extensive gasket layers, the shortened gasket layer leavingfree an outer edge region, which does not comprise the bead, of therelatively extensive gasket layer, wherein at least one structuring isprovided in one of the gasket layers, in a region of the gasket in whichthe shortened gasket layer is present or directly laterally adjoiningthis region adjacent to the position of the bead, said at least onestructuring protruding beyond at least one surface of the gasket layerand consisting of a large number of alternating elevations anddepressions which are introduced into the gasket layer, and in that thestructuring is present at least in certain portions in thecircumferential direction around the through-opening.
 26. The metallicflat gasket according to claim 25, wherein it has its largest overallthickness in the compressed state in the region of the structuring. 27.The metallic flat gasket according to claim 25, wherein the height ofthe structuring changes in the circumferential direction around thethrough-opening.
 28. The metallic flat gasket according to claim 25,wherein the structuring is present only in certain portions in thecircumferential direction around the through-opening.
 29. The metallicflat gasket according to claim 25, wherein the structuring is presentbetween the bead and through-opening or on the side of the bead that isremote from the through-opening or on both sides of the bead.
 30. Themetallic flat gasket according to claim 25, wherein the structuring isconfigured in a strip-like manner and in particular in the form of anannular segment.
 31. The metallic flat gasket according to claim 25,wherein the elevations and depressions are configured linearly,preferably in the form of concentric rings or ring segments, and producean undulatory structure or are arranged on at least one set of virtualstraight lines extending substantially parallel over the total extent ofthe structuring, or extend along at least two intersecting sets ofvirtual straight parallel lines and in particular along virtual straightlines intersecting at right angles.
 32. The metallic flat gasketaccording to claim 31, wherein the depressions are embossed into thegasket layer, the thickness (D₃₆) of the gasket layer preferably beingreduced in the flank region relative to the thickness (D₃₁) of thisgasket layer in the region of the elevations or depressions.
 33. Themetallic flat gasket according to claim 25, wherein the structuring isconfigured in the shortened gasket layer.
 34. The metallic flat gasketaccording to claim 25, wherein the structuring is configured in at leastone of the relatively extensive gasket layers.
 35. The metallic flatgasket according to claim 34, wherein the structuring overlaps theshortened gasket layer.
 36. The metallic flat gasket according to claim35, wherein the height of the structuring is from 0.01 and 0.1 mm,preferably from 0.01 to 0.05 mm.
 37. The metallic flat gasket accordingto claim 34, wherein the structuring does not overlap the shortenedgasket layer.
 38. The metallic flat gasket according to claim 37,wherein the height of the structuring is from 0.09 to 0.50 mm,preferably from 0.1 to 0.4 mm.
 39. The metallic flat gasket according toclaim 25, wherein fastening means openings are present in the at leastone relatively extensive gasket layer and the structuring has a lowerheight in regions in proximity to the fastening means openings than inregions more remote from the fastening means openings.
 40. The metallicflat gasket according to claim 25, wherein it has a plurality ofthrough-openings each surrounded by a bead and the structuring islocated in the region between adjacent through-openings.
 41. Themetallic flat gasket according to claim 25, wherein the shortened gasketlayer is configured in a spectacle-like manner.
 42. The metallic flatgasket according to claim 25, wherein it has two or more relativelyextensive gasket layers.
 43. The metallic flat gasket according to claim42, wherein the structuring is provided in a first of the relativelyextensive gasket layers, in particular a gasket layer which is planarapart from the structuring, and the bead in a second of the relativelyextensive gasket layers, or the structuring and bead are present in thesame relatively extensive gasket layer.
 44. The metallic flat gasketaccording to claim 42, wherein the relatively extensive gasket layershave mutually complementary beads and in particular beads which arearranged in a mirror-inverted manner with respect to one another. 45.The metallic flat gasket according to claim 25, wherein the bead changesat least one of the following properties in the circumferentialdirection: its cross-sectional shape, its height, its width, the changepreferably taking place in such a way that the rigidity of the beadincreases with increasing distance from fastening means openingssurrounding the bead.
 46. The metallic flat gasket according to claim25, wherein namely a gasket in the region of an internal combustionengine or exhaust tract, in particular an exhaust gas manifold gasket orcylinder head gasket, in which the through-openings correspond tocombustion gas openings or combustion chamber openings.
 47. The metallicflat gasket according to claim 46, wherein the gasket is a cylinder headgasket on the surface of a motor block, wherein the structuring isarranged above a region of the motor block in which said motor block hasa lower component rigidity than in other regions, in particular above aweb region between adjacent cylinder bores.
 48. The metallic flat gasketaccording to claim 46, wherein the gasket is a cylinder head gasket onthe underside of a cylinder head, wherein the structuring is arrangedbelow a region of the cylinder head in which said cylinder head has alower component rigidity than in other regions, in particular in aregion concentric with the combustion chamber openings.